Existing brick veneer wall Zone 4A
What is the effective strategy for increasing the R-value for an existing brick veneer wall over 1″ airspace over 1/2″ fiberboard sheathing(w/o WRB) over 2×4 studs with old not full depth fiberglass insulation between and plaster over gypsum lath finish? Given the generally excellent condition of the interior plaster I am unwilling to remove and re-insulate. Can a spray foam be used in the airspace injected from the exterior?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
We have about a thousand of these houses here in Charlottesville, VA and there's no good way to do this that I'm aware of. The brick veneer is quite a hindrance to increasing the R-value. You absolutely SHOULD NOT insert spray foam into the 1" air space. The air space decouples the brick veneer from the sheathing in order to prevent moisture soaked up by the brick from transferring to the sheathing.
One client I'm working with is considering taking down the brick in order to add a layer of insulation outside of the existing wall. This will not be cheap.
You certainly should not fill the air space, as John says it's there for a reason. You don't say where you are in your renovation process but wall insulation upgrades should be about last on your list: reliable solutions will be disruptive, expensive and offer lower ROI than other avenues. I wouldn't recommend taking it on until you have a sealed and insulated crawl space/basement, as much insulation as you manage in your roof (as much as R60 in Zone 4), top-quality mechanicals, and upgraded doors and windows: approximately in that order.
John and James have given you good advice.
Here's one more tip: if your house is air conditioned during the summer, it's important to remember that installing vinyl wallpaper at your house would be very dangerous. The wall assembly you describe is subject to inward solar vapor drive during the summer, so it's important to keep the interior finishes vapor-open.
John, James, and Martin: Thank you for your input.